Isomerization process



1948- w. SWERDLOFF I ISQMERIZATIQN PROCESS Filed Nov. 6, 1944 Irv Hm ,m

mm MN 7 w Wm W A Patented Feb. 17, i948 ISOMERIZATION PROCESS Will Swerdlofi, Dallas, Tex., assignor, by mesne assignments, to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York Application November 6, 1944, Serial No. 562,108

9 Claims.

The present invention relates to an improved method for isomerizing normal parafiinic hydrocarbons in the liquid phase with the aid of hydrocarbon soluble catalysts. More particularly, this invention relates to an improved method for isom-' erizing normal parafiins of from four to seven carbon atoms with the aid of aluminum bromide catalyst, the process being carried out in separate stage reactors.

The isomerization of parafiin hydrocarbons, particularly normal butane by means of hydrocarbon soluble catalysts such as aluminum bromide is well known. Isomerization is a reversible reaction and, as the amount of branched chain isomer product formed increases in the reaction mixture, the rate of reaction slows down. Various methods of increasing the rate of isomerization as the concentration of the isomer builds up and as the activity of the catalyst goes down have been suggested. For example, one method is to separate the conversion into stages and to increase the temperature of the reactant in the secondary and succeeding reaction zones in order to compensate for reduced catalyst activity. Another method is to increase the amount of catalyst promoter in the latter stages. I have taught and claimed in my co-pending application entitled Hydrocarbon conversion process, Serial 527,185, filed March 20, 1944, a third method involving the increase in concentration of the aluminum bromide catalyst as the reaction slows down.

The use of hydrocarbon soluble aluminum bromide catalyst for isomerizing straight chain paraifins to branched chain parafiins, particularly for converting normal butane to isobutane in liquid phase operation, has certain advantages partlcularly if the conversion is carried out in separate stages. Better contact of the catalyst with the normal butane reactant is obtainable than in processes utilizing relatively insoluble catalyst such as aluminum chloride. However, in utilizing separate stages there are certain disadvantages among which is the concentration of too large amounts of catalyst in a latter stage or stages which results from the heretofore procedure of transferring the reaction mixture from the primary reaction zone to the secondary reaction zone and thence to succeeding stage reaction zones as a liquid. As this solution of catalyst becomes more concentrated it becomes more difficult to handle, not only in pumping to provide circulation and contact in the last stage of conversion but particularly in pumping from the catalyst concentrator from which the isomerized prodnot is flashed following the last stage of conversion. This method of catalyst concentration is described in the above co-pending application. The chief difficulty in pumping the highly concentrated solution of catalyst is that the concentrated solution tends to foul packing glands as a result of deposition of precipitated catalyst.

It is an object of the present invention to carry out the isomerization of parafiinic hydrocarbons in the presence of hydrocarbon soluble catalyst in stages in such a manner that the catalyst will not be concentrated in the latter stages of the conversion process. Another object of this invention is to transfer the hydrocarbon reactant and product of conversion from the primary stage reactor to succeeding stage reactors in a multi-stage isomerization process employing a soluble catalyst, in a fluid stream substantially free of said soluble catalyst. A further object of the invention is to operate a multistage butane isomerization process utilizing hydrocarbon soluble aluminum bromide catalyst in such a manner that the transfer of butanes from the reaction zones is made substantially in the vapor phase. An additional object of the invention is to operate a multistage butane isomerization process utilizing aluminum bromide catalyst in such a manner that no separate catalyst concentration step is required for the separation of the soluble catalyst from the product for recycle to the reactors.

To accomplish these objects, as well as other objects, which will be apparent from a full understanding of the invention to be more fully described, I propose to operate the series of two or more reaction stages maintaining a temperature and pressure gradient between each of these stages, the highest temperature and pressure being maintained in that reactor to which fresh feed is initially admitted. A feed stock comprising, for example, predominantly normal butane, containing from about 1 mol percent to about 5 mol percent of aluminum bromide, is passed to theprimary reaction zone which is preferably a tower packed with inert material such as unglazed ceramic ware. The liquid normal butane in the primary reaction zone is partially converted to isobutane. The product is vaporized and isobutane vapors together with unconverted butane vapors pass overhead to a second reaction zone where the temperature and pressure are preferably maintained at somewhat lower level. Vapors more highly enriched with respect to isobutane from the second reaction zone may be transferred to a third reaction zone which is operated in the same manner as the second reaction zone except that a lower temperature and a lower pressure may be maintained than in the second zone. The vapor product from the third or last zone is passed to a fractionation system for recovery of isobutane and for the separation of normal butane recycle.

Referring to the drawing, towers l, 2 and 3 are a series of reactors,"preferablypacked with inert ceramicware. These reactors are operated substantially full of liquid butane containing about 2.5 mol percent of dissolved aluminum bromide catalyst and liquid level controllers 4, 5 and 6, which control the rate of vaporization or discharge from the towers as hereinafter described, are provided to maintain substantially the same level of liquid butane-iii the three towers. Fresh normal butane feed is passed by means of pump in line ll through heater [2 where it is heated to a temperature preferably within the range of 209 F. and 250 F. 'From heater 12 the hot butane stream passes via line l3 to reaction tower "i, which may be operated at a temperature within the range of. 175 F. and 275 F. and at a pressure just sufficient to maintain liquid phase conversion. Although the isomerization of normal butane to isobutane is slightly exothermic, s uflicient, heat. must be supplied to reaction tower I to continuously vaporize the butane product and hence heating means it is provided at the base of,t ower l The rate of evaporation from tower l is controlled by level controllerd which regulates the heat available for evaporation. The maximum residence time for which the system can be operated is determined by the dimensions and number ofthe reaction vessels. Shorterresidenc. times can be obtained by lowering the. liquid level maintainedin the reaction vessel. Total overall residencetimes ofgfliOm. about one-half hour to aboutten hour sjor the series 01 reactors are suitable, choice within range depending on l1.1% ac i i he talystas a fe ed y t perature, concentration f;cat a lyst and catalyst promoter, and efl ipiencyof contact. of the promoter with the reactant butane and dissolved catalyst. Intimate contact is obtained by circu1ation of the reactant proyidedby pump is in circulating line IQ.

which connects with circulatir1gline.I5 the fresh catalyst being added to replace spent; catalyst which is withdrawn as an insolubletar through bottom drawofi line IS,

The vaporfrom tower l consists ofa mixture of isobutane product and unconverted normal.

range of from about l75 F., to about 250 and at a pressure suificient tomaintain the reactants in the liquid phase. The average temperature in tower 2 -wi l l usua1 ly be from 5 to,

35 F.lower than t-hetemperature in tower i. A part of the vapor in line 30 r nay be condensed in condenser 3|, this method-,bfiillgused to with.- draw the exothermic heatofthe isomerization reaction from the system. Heat .is withdrawn from the vapors by controlled how of coolant through condenser 3|..at least a part of the vapors being condensed andthefiowof coolant being regulated .in cooperation; with liquid "level Fresh aluminum bromide catalyst is provided through line H. and line i3.

controller 5 at the top of tower 2. The amount of cooling and condensing may be regulated by liquid level fluctuation in tower 2. If desired, condenser 3! may be omitted in which case the vapors pass through line 32 and are introduced directly to tower 2. Either of these methods of operation permits utilization of the heat of condensation of the gaseous product to vaporize isobutane and unconverted normal butane in tower 2." Mixing and contacting of the reactants with catalyst and promoter are improved by omission of condenser 3|. The bubbles of rising vapor serve to agitate. the contents of the tower, es'-- pecially near the bottom, before they are com-- pletely absorbed in the liquid reactant. When operating with no' condensation of vapors from tower l excess heat is removed from tower 2 by means of a cooler in circulating line 33 (not shown) through which the flow of coolant is regulated by liquid level controller 5. Alternatively, the vapors from tower l may be completely condensed and introduced into tower 2 as a lid: uid, in which case heat would have to be supplied to tower 2 to, vaporize the product. Fresh. lu inum bromide ata yst is supp ed; to towel. 2 through line H. and line 34 which connects with line 33 and spent catalyst tar is withdrawn. from tower Zvia line 35-.

Tower 2 is provided with baflie 36 and; drip pan 31. Vapor in equilibrium with the liquid-in tower 2 passes via overhead line 40 to tower 3 which is operated at a, temperaturewithin therange of F. to about 225 FL, and fromfif to- 35 lower than the temperature. in tower 2. The; pressure in tower 3 is lower than the pressure maintained in tower 2 and is sufiicient to maim-v tain liquid phase operating conditions. As. in. the case of vapors from tower 2, the vaporsin line so may be partially condensed or the cone, denser may be omitted and the liquid level and the temperature in tower 3 may be controlled}v by cooler 41 in circulating line 42;provided,with.. pump 43. Fresh aluminum bromide catalyst. is: introduced to towers-via lines Hand 44 .and.cir-, culating line 42 to replacev spent aluminum bro-r. mid catalyst which is withdrawn as. a tar, through line 45. Promoter for the catalyst in.v towers I, 2 and 3 maybe introducedvia lines. 4] and 48, 41 and 4.9, and by line and line..50't.-. which connect with the mainfeed lines to the. respective towers. If desired, the. promoter, which may be hydrogen bromide, bromine, alkyl bromide, oxygen or other activator. for alumle num bromide catalyst, may. be introduced along-.'. with the catalyst or directly to. the. towers indee pendent of the feed stream. However, I prefer. to add the activator in a, stream. separate. from. the catalyst. If desired, the amount of activatora. may. be adjusted in towers 2 andi3 to atleast. partially compensate for reduced conversion. caused by the. higherisobutane content of the. reactant and lower temperature of. operation in. these towers.

The isobutane richvapor is substantiallyfreedof entrained liquid by. baffle 5| in the topoi? tower 3 and passes. via line .69 to condenserlm through pressure release valve 62 and is fraction-'- ated in fractionation system 63. Isobutane ands any lower boilinghydrocarbons are withdrawn by: line E i and iso Cs and higherboiling hydrocarbons, if any, are withdrawn through line 65hr incorporation in aviation fuel or motor fuel Normal butane recycle is withdrawn through line 58 and is recycled to fresh feed line H. The compositionof the recycle stream in line 66 willan ampere...

proximate the composition or the 'fresh 'feed stream, that is for example, isobutane approxil mately 1.5 percent, normal butane 97 percent and isopentane 1.5 percent.

-While I have described my process as operating to produce isobutane from a normal butane stream in a three stage reactor system, obviously two or four or more reactors in series may be used. Also, I may isomerize pentanes and even.

higher boiling normal paraflins by my process. Thus, parafiinic hydrocarbons having boiling points sufficiently low or parafiinic naphthas having distillation endpoints sufficiently low to permit complete vaporization under the conditions of operation of my process, may be isomerized by this improved method. For example, normal parafiins or mixtures thereof from normal butane through normal octane may be processed within the above temperature range and even nonane and decane may be isomerized at higher temperatures at shorter residence time by this method of operation.

verting normal butane to isobutane, I may feed substantially pure normal butane of the above specified composition to tower I. With a temperatureof 200 F. and a residence time of 2 hours in tower l the overhead in line so will approxi- As a specific application of the process for conmate 14.6 mol percent isobutane, 83.9 mol percent 1.5 mol per cent 150 C5 assuming a residence time By further in tower 2 equal to that in tower l. processing this isobutane enriched product in tower 3 at a temperature of 180 F. and at a pressure of about 155 pounds per square inch for the same residence time, I am able to deliver to fractionator 53 a stream containing approximately 35.7 mol percent isobutane, 62.8 mol percent normal butane and 1.5 percent isopentane. By operating at higher temperatures in the range of about 225 F. to 250 F., I may obtain higher conversion in each zone and deliver to fractionator system 63 a mixture of butanes much richer 1n isobutane. The choice of temperature of operation of towers I, 2 and 3 will be governed by the extent of cracking and disproportionation that:

can be tolerated, as well as by the eiTect of term perature 0n catalyst life. Temperatures as high as 250 F. are desirable and even at 275 F. cracking is not extensive if the residence time is held in the lower range of the above limits.

As stated hereinabove my soluble catalyst isomerization process has the advantage of eliminating the necessity of a catalyst recycle step. The conversion in each step may be regulated independ-.

ently thus allowing the free choice of catalyst con centration and activator concentration. Another advantage of my process lies in the possibility of obtaining a high conversion rate in the first stage in the presence .of relatively low isobutane concentration in the liquid and utilizing mild conditions in the latter stage conversion steps where the isobutane concentration is relatively high, thus avoiding disproportionation and cracking. This is made possible by adding catalyst and pro.- moter in separate independent streams to the separate stages. Closely related to this advantage is theadvanta e btainedl y in 10W 9 1 version in the first reaction zones of the series and. obtaining successively higher isobutane concentration in the overhead products from the suc-: ceeding reaction zones, thus building up the iso-.. butane concentration of the isomate in the final effluent passing to the fractionation system and; obtaining easier separation of the isobutane in; said fractionation system. This desirable concentration gradient of isobutane in the series of reactors is brought about as a result of a dual functioning of the individual reaction zones to the extent that the concentration of isobutane is in-: creased both by the isomerization reaction and as a result of the vaporization. Advantage is taken of the lower boiling point of the isoparafiin prod uct.

gravating pump corrosion problems.

Obviously many modifications and variations: of the invention, as hereinabove set forth, may 5 be made without departing from the spirit and scope thereof, and therefore only such limitations... should be imposed as are indicated in the ap-,;;

pended claims.

I claim:

1. A continuous liquid phase stepwise process; for isomerizing at least-one normal parafin hydrocarbon containing at least four carbon atoms: per moleculein the presence of aluminum bromide catalyst dissolved in said hydrocarbon 5 wherein the reaction is carried out in at least two perature in the next succeeding stage at isomerization conversion level and to vaporize isomer-f ized paraffin hydrocarbon and unreacted nor--.

mal paraiiln hydrocarbon product from the hydrocarbon solution of said catalyst in said suc-J ceeding stage by introducing at least a portion of the hydrocarbon removed from the primary zone into the liquid hydrocarbons in the succeed-f ing reaction zone as a vapor without intermediate condensation thereof.

2. A continuous liquid phase multistage isomerization process whereby at least one normal hydrocarbon is isomerized to al branched chain hydrocarbon having the same parafiinic number of carbon atoms as said normal parafiinic hydrocarbon in at least two separate stage re-' action zones comprising a primaryisomerizationf zone and at least one additional separate isomer-' ization zone in the presence of aluminum bromide" catalyst dissolved in said paraffinic hydrocarbon and in the presence of an activator for said cat-f alyst comprising the steps of (1) continuously' feeding to said primary isomerization zone a Stillanother advantage of my process is the: elimination of catalyst concentration for recycle; As stated hereinabove a concentrated solution of j aluminum bromide tends to deposit aluminum' bromide in pump packing glands thereby ag- 7, iz'lng from said primary reaction zone. unreacted normal paraflinic, hydrocarbonv and branched chain isomerlzed hydrocarbon product, (4) continuously transferring at least. apart oi the hydrocarbon vapor formed in step 3. to said, separalu:v isomerization zone without intermediate. condone sation, controlling the proportion of said by! drocarbon vapor of step 4 condensed in the senarate'reaction zone to maintain the liquified hydrocarbon product in said separate zone ata tom perature below the isomerization temperature maintained in the primary reaction zone, (6 add? ing separate streams of aluminum bromide catalyst and catalyst activator to said separate stage,

reaction zone, (7) continuously vaporizing from the hydrocarbon solution of aluminum bromide in said separate reaction zone a mixture of hydrocarbon vapors comprising branched chain paraifinic hydrocarbon and unreacted normal paraffinic hydrocarbon, and (8) continuously passing the vaporized hydrocarbon mixture sub?- stantially free of aluminum bromide catalyst from step '7 to a fractionation zone to separate a fraction consisting essentially of said branching chain parafiinic hydrocarbon from a fraction consisting essentially of unreacted normal straight chain parafiinic hydrocarbon.

3. A multistage liquid phase catalytic process for the isomerization of at least one normal parailinic hydrocarbon having at least four carbon atoms and not more than eight carbon atoms per molecule which comprises the steps of (1) passing a liquid stream of said hydrocarbon to the first of a series of reaction zones, (2) introducing to said first reaction zone separate streams of a hydrocarbon solution of aluminum bromide catalyst and an activator for said catalyst, (3) maintaining the temperature in said first reaction zone at isomerization conversion level and maintaining a pressure in said zone sufficient to provide therein liquid phase contact of the hydrocarbons with aluminum bromide catalyst, l) vaporizing unconverted normal parammo-hydrocarbon and isomerlzed parafiinic hydrocarbon from the hydrocarbon solution of aluminum bromide in said first reaction zone, (5) condensing a part of said hydrocarbon vapors from step 4, (6) introducing both the hydrocarbon liquid and the residual vapor product of step 5 into the liquid hydrocarbons in the next succeeding reaction zone, (7) introducing to said next succeeding reaction zone separate streams of hydrocarbon solution of aluminum bromide, catalyst and of activator, (8) controlling the heat, ofcondensation available from step 6 by adjust ing the extent of condensation of hydrocarbon vapor in step 5 to maintain isomerization conditions of temperature in said next succeeding reaction zone and to furnish the heat for the vaporization of a mixture comprising isomorized paraflinic hydrocarbon and unconverted normal parafiin hydrocarbons from the solution of aluminum bromide in said next succeeding zone, (9) passing the vapor mixture obtained from said succeeding reactor in step 8 to at least one succeeding reaction zone via an intermediate partial condensation step as described in step 5 and processing the vapor-liquid mixture according to the procedure described in steps 6, '7, and 8, and (10) passing the vapor efiluent from thelfinal isomerization stage of the process to a iractionation zone for recovery of at least one isomerlzed hy-' drocarbon and for separation of at least one normal parafiinic hydrocarbon for recycle to step 1- of the process.

A ulti ta liquid phase catalytic process for the isomerization of norma butane. which comprises the stepsoi: (l); passing: a liqu d s ream.

normal butane and, isobutane product from the yd ocarbon solution of aluminum bromide in said first reaction tower, (5) condensing apart of the hydrocarbon vapors from step 4, introducing both the hydrocarbon liquid condensate of step 5. and the residual vapor product of step 4, into the liquid butanes in the next succeeding reaction tower, (7) introducing into said next succeeding packed reaction tower separate streams of butane solution of aluminum bromide catalyst and activator, (8) controlling the heat of condensation available from step 6 by controlling the extent of condensation of hydrocarbon vapor in step. 5 to maintain isomerization conditions of temperature in said succeeding reaction tower and to furnish the heat necessary for the vapor! ization of the mixture comprising isobutane and normal butane from, the butane solution of aluminum bromide, (9) passing the vapor effluent from the final isomerization tower to a fractionation zone for recovery of isobutane.

5. In a continuous liquid phase multi-stage process for the isomerization of normal butane to isobutane in the presence of butane dissolved aluminum bromide catalyst wherein the reaction is carried out in a series of at least two separate stages, the improvement which comprises trans! ferring unreacted normal butane and isobutane product as a vapor mixture substantially free of aluminum bromide catalyst from the primary stage to the secondary stage and absorbing without intermediate condensation at least a part of said vapor mixture in the butane solution of aluminum bromide catalyst in said secondary stage whereby at least a partof the heat of condense tion of said vapor mixture is utilized to maintain the temperature in said secondary stage at isomerization conversion level and to separate as a vapor isobutane and unreacted normal butane product from aluminum bromide catalyst in said secondary stage.

6. A continuous liquid phase isomerization process wherein a normal paraiiinic hydrocarbon having at least four carbon atoms but not more than eight carbon atoms is converted to the corresponding branohed chain hydrocarbon in the presence of dissolved aluminum bromide catalyst in at least two stages comprising a primary isomerization zone and at least one additional separate isomerization zone comprising the succes solution of aluminum bromide in said primary reaction zone, (4) transferring the hydrocarbons vaporized in step 3 to said separate isomerization zone, (5) maintaining said transferred hydrocarbon in said separate isomerization zone in liquid phase at a temperature and pressure below the temperature and pressure maintained in said primary isomerization zone and in the presence of dissolved aluminum bromide separately added to said additional separate isomerization zone, (6) continuously vaporizing a mixture of isomerized hydrocarbon and unreacted normal paraflinic hydrocarbon from the liquid in said separate isomerization zone, and (7) passing the vaporized mixture from step 6 to a fractionation zone for separation of a fraction comprising predominantly branched chain hydrocarbon from a fraction comprising predominantly normal straight chain parafiinic hydrocarbon.

7. The process as described in claim 6 wherein at least a part of the heat of condensation of the vapor from the primary isomerization zone is used in direct heat transfer to maintain the temperature in said separate isomerization zone and to evaporate the mixture of isomerized hydrocarbon and normal paraffin hydrocarbon from the liquid in said separate isomerization zone.

8. The process as described in claim 6 characterized by the added improvement comprising the separate addition to of aluminum bromide catalyst promoter.

the isomerization zones 3 9. In a continuous multi-stage process for the isomerization of at least one normal paraffin by drocarbon by means of'a catalyst soluble in said parafiin hydrocarbon under isomerization conditions wherein the reaction is carried out in a series of at least two separate isomerization zones in the liquid phase, the improvement which comprises vaporizing the partially isomerized mixture of paraffin hydrocarbons in each reaction zone for transfer to the next succeeding zone and maintaining and controlling the level of liquid hydrocarbons in any isomerization zone following the primary isomerization zone by condensing at least a part of the vapor mixture of hydrocarbons from the next preceding isomerization zone of the series and withdrawing at least a part; of the heat of condensation before passing the hydrocarbons to the succeeding isomerization zone in which said liquid hydrocarbon level is maintained and controlled.

WILL SWERDLOFF'.

REFERENCES CITED The following references are of record in the 

